As a power supply for a laptop personal computer (hereinafter, referred to as a “PC”) and other information processing apparatuses, a power supply circuit that obtains a direct current (DC) output from an alternating current (AC) adapter power supply and that supplies power to the information processing apparatus has been used.
The common AC adapter used for PCs today takes the form of a constant voltage power supply circuit, and its output is kept constant with respect to changes in the AC input. Meanwhile, as devices become smaller, a smaller size has become required for the AC adapter as well. In addition, in regard to its output power, there has been a demand for a large-capacity output together with power-saving efforts, along with improvements in the performance and functions of information processing apparatuses. In such a situation, thermal design of the AC adapter involves a greater difficulty today.
For a conventional AC adapter, a prescribed constant output power is required both when environmental conditions are at the worst or when they are not. The difficulty in design is how to make the maximum power that may be output under the worst environmental conditions the rated power, and how to derive it.
Incidentally, our country experienced the unprecedented Great East Japan Earthquake, which involved not only earthquakes and tsunamis but also the destruction of nuclear power plants, as well as secondary disasters such as the radiation leakage and evacuation from designated zones, leading to a limited power supply capability due to the destruction of the nuclear power plants.
A bitter lesson learned from these experiences is that the power supply is not inexhaustible, and that continued enhancement of low-cost supply of power so as to respond to the demand without considering the means is difficult now. Therefore, it is necessary for industries that provide electronic devices to provide an apparatus with flexibility in response to the environment in which it has to operate by effectively using what little power is available.
In response to such a demand, a technique is known in which a power supply control circuit that controls the output of a power supply is configured to be equipped with a setting unit that performs variable setting of the maximum rated output according to input temperature information (the technique described in the Document 1 for example).
However, conventionally, there has been a problem wherein it is impossible to notify the device of the power-receiving side of restrictions due to environmental conditions in a power apparatus, and it is impossible to perform cooperative operations between the power apparatus and the receiving device according to the environmental conditions.    Document 1: Japanese Laid-open Patent Publication No. 2001-75659.